1. Field of the Invention
This invention relates to rotating x-ray anode tubes and in particular to the joining of the anode disc to the anode stem.
2. Description of the Prior Art
The anode assembly of a rotating x-ray anode tube consists of an anode disc comprising a tungsten-rhenium alloy target joined to a base, or substrate, comprising either a molybdenum or molybdenum-tungsten alloy. The anode disc is joined to a stem which, in turn, is attached to the rotor of an induction motor. The stem may be of columbium.
A method for joining the substrate to the stem includes cold forming followed by a heat treatment to produce a diffusion bond between the components. However, to achieve a good diffusion bond one must practice good process steps of adhering to precise measurements and adherence to good cleanliness habits. The dimensions of the outside diameter of the stem and the inside diameter of the hole in the substrate must be maintained very closely. Ideally an interference fit is provided to produce a good diffusion bond. Such a fit is dependent upon degree of surface finish, and surface cleanliness. Should the initial extent of intimate contact between the stem and the substrate of the disc be less than desired, a poor, or incomplete, diffusion bond may result. An incomplete bond between the stem and the disc constitutes a structural flaw. Such a flaw, under the influence of rotational stresses and, more importantly, cyclic thermal stresses can nucleate a catastrophic failure of the anode disc.
It is therefore an object of this invention to provide a new and improved method for joining the stem to the substrate of the disc of an anode assembly.
Another object of this invention is to provide a two step inertia welding process to make anode assemblies for rotating x-ray anode tubes.
Other objects of this invention will, in part, be obvious and will, in part, appear hereinafter.